Abstract: An analysis system features a confinement device, an optical measurement device, a flow device, a collecting conduit, and an actuation device. The confinement device comprises a measurement chamber, optically transparent first and second measurement surfaces that face each other across a distance that defines a thickness of the measurement chamber, and a flexible membrane that forms a seal with the measurement surfaces to laterally delimit the measurement chamber. When the collecting is sealed with a container, a connection is established that permits a liquid sample to be collected from the container. The optical measurement device emits light towards the chamber and detects light that has been transmitted through it, wherein the flow device causes liquid to flow through the collecting conduit between the container and the measurement chamber. The actuation device varies the thickness.